1、Designation: D4526 96 (Reapproved 2007) D4526 12Standard Practice forDetermination of Volatiles in Polymers by Static HeadspaceGas Chromatography1This standard is issued under the fixed designation D4526; the number immediately following the designation indicates the year oforiginal adoption or, in
2、the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. Asuperscript epsilon () indicates an editorial change since the last revision or reapproval.1. Scope*1.1 Headspace gas chromatography (GC) involves the determination of volatile components
3、 in a polymer solution by gaschromatography of a vapor phase in thermal equilibrium with the sample matrix. Volatiles in finely ground insoluble polymers canalso be determined with and without an extracting solvent.1.2 This practice provides two procedures:1.2.1 Procedure AAutomatic headspace analys
4、is.1.2.2 Procedure BManual injection headspace analysis.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibilityof the user of this standard to establish appropriate safety and health practices and determine the applicability
5、 of regulatorylimitations prior to use. Specific precautionary statements are given in Section 6.NOTE 1There is no equivalent ISO known ISO equivalent to this standard.2. Referenced Documents2.1 ASTM Standards:2D4322 Test Method for Residual Acrylonitrile Monomer Styrene-Acrylonitrile Copolymers and
6、 Nitrile Rubber by HeadspaceGas Chromatography (Withdrawn 2010)3E260 Practice for Packed Column Gas ChromatographyE355 Practice for Gas Chromatography Terms and RelationshipsE594 Practice for Testing Flame Ionization Detectors Used in Gas or Supercritical Fluid Chromatography3. Significance and Use3
7、.1 For various reasons, one may want to measure the level of unreacted or residual monomer, water, or other volatilecomponents in a polymer sample.3.2 Volatiles of interest are often at trace concentrations. Headspace analysis is suited for determination of these tracecomponents which often cannot b
8、e determined by conventional gas chromatography because of sample decomposition orinterferences.3.3 For polymer analysis, sample treatment for headspace analysis is simpler than conventional gas chromatography, whereprecipitation steps may be required to prevent polymer contamination of the chromato
9、graphic column.3.4 This headspace practice will be able to determine qualitatively any component with sufficient vapor pressure. It is capableof yielding semiquantitative results and can be used for relative comparisons between samples.4. Apparatus4.1 Gas Chromatograph, equipped with an appropriate
10、detector and backflush valve.4.1.1 For Procedure A, an Automated Headspace Sampler,4,5 including backflush capability, thermostated sample tray, andassociated accessories fulfill these requirements while providing for automatic sequential sampling of headspace vapors.1 This practice is under the jur
11、isdiction of ASTM Committee D20 on Plastics and is the direct responsibility of Subcommittee D20.70 on Analytical Methods.Current edition approved Sept. 1, 2007Dec. 15, 2012. Published November 2007December 2012. Originally approved in 1985. Last previous edition approved in 20012007as D4526 - 97(20
12、01)(2007).1. DOI: 10.1520/D4526-96R07.10.1520/D4526-12.2 For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at serviceastm.org. For Annual Book of ASTM Standardsvolume information, refer to the standards Document Summary page on the ASTM website.3 T
13、he last approved version of this historical standard is referenced on www.astm.org.4 The sole source of supply of the apparatus known to the committee at this time is Perkin-Elmer Corp., Main Ave., Norwalk, CT 06856.This document is not an ASTM standard and is intended only to provide the user of an
14、 ASTM standard an indication of what changes have been made to the previous version. Becauseit may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current versionof the standard as publis
15、hed by ASTM is to be considered the official document.*A Summary of Changes section appears at the end of this standardCopyright ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States14.1.2 Procedure B requires the following additional equipment:4.1.2
16、.1 Constant-Temperature Bath, capable of maintaining 90 6 1C.4.1.2.2 Gas-Tight Gas Chromatographic Syringes, which can be heated to 90C for sampling and injection.4.1.2.3 Valve, 6-port for backflush assembly.NOTE 2Appropriate detectors could include the following:(a) Flame ionization (FID) for gener
17、al organic volatiles,(b) Electron capture (EC) for halogenated species,(c) Nitrogen-phosphorous (NPD) for acrylonitrile,(d) Thermal conductivity (TC) for water, and(e) Hall electroconductivity or photoionization (PID) for vinyl chloride.4.2 Chromatographic Columns:4.2.1 Packed Column AnalysisColumn
18、packings5,6 found to be useful for residual monomers (for example, acrylonitrile, vinylchloride) include Chromosorb or Porapak porous polymer packings, 0.4 % Carbowax 1500 liquid phase on Carbopak C support,or 0.19 % picric acid on Carbopak C support. Other columns can be used after it is determined
19、 that they give the required resolutionand accuracy for the component of interest.4.2.2 Capillary Column AnalysisChoose a column capable of achieving the required resolution for the components of interest.For example, for acrylonitrile monomer, the column of choice is a Quadrex 0072, 25m 0.32mm inte
20、rnal diameter fusedsilica.5,74.3 Integrator, recorder (5mV full scale), computing integrator or appropriate computer data station and software capable ofmeasuring and storing peak area data.4.4 Headspace Vials, septa, ring closures, and vial sealer.4.5 Analytical Balance, capable of weighing to 60.0
21、001 g.4.6 Soap Film Flowmeter and Stopwatch, or other means of measuring gas flow rates.4.7 Pressure Regulators for all required gas cylinders.4.8 Filter-Dryer Assemblies for each required gas cylinder.5. Reagents and Materials5.1 Solvent, Reagent Grade, or Best AvailableThe solvent should be free o
22、f interferences at the retention time of volatilecompounds determined by this technique. Typical polymer solvents include water, dimethylformamide (DMF), dimethylacetamide(DMAC), propylene carbonate, and o-dichlorobenzene. These solvents are readily backflushed from most chromatographiccolumns.NOTE
23、3Volatile contaminants can often be removed by sparging with an inert gas for 24 to 48 h.5.2 Nitrogen, oxygen-free.NOTE 4Helium may also be used as the carrier gas and argon/methane is the preferred carrier gas for use with electron capture detectors.5.3 Hydrogen, prepurified, for use with flame ion
24、ization detectors.5.4 Air, breathing or water pumped, for use with flame ionization or nitrogen-phosphorus detectors.5.5 Standards, best available, for volatile compounds to be analyzed using this technique.6. Safety Precautions6.1 Volatiles such as vinyl chloride and acrylonitrile should not be rel
25、eased to the laboratory atmosphere. Prepare standards andhandle samples in a well-ventilated fume hood.6.2 Some of the recommended solvents are flammable. Dimethylacetamide is also absorbed through the skin, so avoid contact.6.3 Be careful not to come into contact with heated chromatograph parts, su
26、ch as the detector, column, rotating sample tray, hotsample bottles, etc.6.4 Once heated, sample vials containing polymer volatiles are under pressure. After analysis, vent the pressure with ahypodermic syringe needle connected to a charcoal slug or vented hood before removing vials from the constan
27、t temperature bath.5 If you are aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at ameeting of the responsible technical committee,1 which you may attend.6 The sole source of supply of the apparatus
28、known to the committee at this time is Supelco, Inc., P.O. Box 628, 146 S. Water St., Bellefonte, PA 16823.7 The sole source of supply of the apparatus known to the committee at this time is Quadrex Corp., P.O. Box 3881, Woodbridge, CT 06525.D4526 1227. Storage and Sampling7.1 To prevent loss of vol
29、atiles from polymer pellets, or resin, store in tightly sealed jars with minimal headspace or heat-sealedpouches constructed of an outer polyester layer, an aluminum foil middle layer, and a polyolefin inner sealing layer.7.2 For rolled polymer film samples, discard 3 to 5 m of film before taking th
30、e sample for headspace analysis because volatilescan be lost by diffusion through the outer film layers.7.3 Powdered resin samples (for example, poly(vinyl chloride) can be weighed directly into a tared headspace vial. A 4-gsample (weighed to the nearest 0.0001 g) should be adequate for determinatio
31、n of many volatiles at the parts per million (ppm)levels using sensitive ionization detectors.7.4 Polymer pellets or granules and film samples can be dissolved, depending on chemistry of polymer, to facilitate attainingthermal equilibrium in a reasonable period of time. These samples are weighed (0.
32、56 0.001 g) into headspace vials, then dissolvedin 10 mL of an appropriate solvent. Using ionization detection, these 5 % solutions provide sensitivity for many volatiles at ppmlevels. Sample size can be increased to attain sensitivity at lower levels.NOTE 5Freeze grinding polymer pellets or granule
33、s with liquid nitrogen and screening through a thirty-mesh screen often works as well as testingpowdered resin. However, some volatiles may be lost even at these low temperatures.NOTE 6This technique of sample preparation requires analysis of the solvent blank to ensure freedom from interferences at
34、 volatile componentretention times.NOTE 7Increased sample sizes can result in viscous solutions. Warming these solutions is often necessary to ensure complete sample dissolution.8. Preparation of the Gas Chromatograph8.1 Refer to Recommended Practice E260 and the operator and service manuals of the
35、instrument being used for detailsregarding column installation, flow rate adjustment, and optimization of detector sensitivity.8.2 Refer to Practices E355 and E594 for information on terms, relationships, and procedures for testing flame ionizationdetectors.8.3 Install the chromatographic column in
36、the instrument oven. If solvent backflush is to be used, the front portion of the columnconsists of a short length (3 ft) connected with a low dead volume tee to the longer analytical column section. Fig. 1 shows a typicalbackflush assembly for a gas chromatograph designed for manual headspace analy
37、sis.8.4 Adjust the carrier gas flow rate to obtain the same column flow in the analysis and backflush chromatographic modes.8.5 Switch off the detector combustion gases before disconnecting the column from the detector to avoid buildup of an explosivegas mixture in the GC oven.8.6 Condition the colu
38、mn at a temperature that is 10 to 20C above the expected operating temperature. With ionizationdetectors, the column should not be connected to the detector during the overnight conditioning period.8.7 After conditioning, connect the column to the detector and optimize detector gas flow (air, hydrog
39、en) for maximumsensitivity.8.8 Set temperatures as follows:8.8.1 Chromatograph Oven (Column), as appropriate.8.8.2 Dosing Needle, 10C above column temperature.8.8.3 Injection Block, 10C above column temperature.8.8.4 Detector, 10C above column temperature.8.8.5 Temperature Bath, 90 to 120C (dependin
40、g on component volatility and rated bath temperature).9. Procedures9.1 Procedure AAutomated Sample Analysis:9.1.1 Prepare sample solutions in accordance with the criteria of Section 7, then equilibrate solutions for at least 1 h in thethermostatted sample tray.9.1.2 Optimize analyzer injection time
41、to give maximum signal. Injection times from 6 to 9 s are suitable for mostdeterminations at the ppm level.9.1.3 Adjust the analysis and backflush times consistent with fast analysis time and freedom from solvent interferences.9.2 Procedure BManual Injection:9.2.1 Prepare sample solutions in accorda
42、nce with the criteria of Section 7, then equilibrate solutions for at least 1 h in aconstant-temperature bath.9.2.2 Using a warm gas syringe, inject 1.0 mL of the equilibrated sample headspace into the gas chromatograph prepared inSection 8.NOTE 8The syringe can be kept warm in a 90C oven between sa
43、mplings.D4526 1239.2.3 Switch backflush valve to VENT position 1 min after elution of the latest volatile component of interest. Backflush timeshould be four times as long as the forward flow time.9.2.4 At the end of the predetermined backflush time, return the valve to the ANALYSIS position.9.2.5 A
44、llow at least 2 min for baseline equilibration between samples.10. Report10.1 Report the following information:10.1.1 Sample identification,10.1.2 Sample preparation; equilibration time and temperature,10.1.3 Method of calibration, and10.1.4 Concentration of desired volatile components.11. Keywords1
45、1.1 gas chromatography; headspace; polymers; volatilesFIG. 1 Typical 6-Port Valve Backflush AssemblyD4526 124SUMMARY OF CHANGESCommittee D20 has identified the location of selected changes to this standard since the last issue(D4526 - 97D4526(2001)-961) (2007) that may impact the use of this standar
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